This invention relates to a method for pumping and heating and/or vaporizing fluid, and particularly cryogenic fluids. Systems for pumping and heating a fluid to a desired temperature are well known in the art. For example, systems are known for heating liquid nitrogen at -320.degree. F. to provide gaseous nitrogen at a desired pressure and temperature, for example 5,000 psi and 70.degree. F. The vaporized nitrogen has many uses, among which is the displacing of fluids in oil wells.
Before the present invention, the known systems used inefficient Otto-cycle engines, burners, direct fired units, boiler systems, and the like, to directly heat the fluid.
Using the heat rejected from internal combustion engines such as Otto-cycle engines to vaporize small quantities of fluid is very inefficient because the work required to pump the fluid is quite small compared to the power rating of the engine which has relatively poor part-load fuel economy. For this reason, these systems are not practical for pumping and vaporizing significant quantities of fluid. Also, these systems do not use readily available diesel engines to produce the heat.
The use of burners and direct-fired units increases the complexity of the system, leading to reduced reliability and potential hazards where flammable or explosive materials are present. Other systems heat the fluid by using the engine coolant water. A hydraulic oil circuit is utilized to increase the load on the heat engine in order to increase the temperature of the engine coolant water with a back pressure generated to further increase the load. However, the disadvantage of such prior system is that the hydraulic pump is oversized in comparison to the hydraulic motor found in the system. This resulted in a large temperature increase in the hydraulic oil itself necessitating a cooling step utilizing the engine coolant water after it had gone through a heat exchange with the fluid. A further disadvantage of such systems is that this useful heat in the hydraulic oil circuit could not be used in a heat exchanger with the cryogenic fluid for fear of freezing the hydraulic oil.